Biogenic synthesis of Ag, Au and bimetallic Au/Ag alloy nanoparticles using aqueous extract of mahogany (Swietenia mahogani JACQ.) leaves.

In this paper, we have demonstrated for the first time, the superb efficiency of aqueous extract of dried leaves of mahogany (Swietenia mahogani JACQ.) in the rapid synthesis of stable monometallic Au and Ag nanoparticles and also Au/Ag bimetallic alloy nanoparticles having spectacular morphologies. Our method was clean, nontoxic and environment friendly. When exposed to aqueous mahogany leaf extract, competitive reduction of Au(III) and Ag(I) ions present simultaneously in same solution leads to the production of bimetallic Au/Ag alloy nanoparticles. UV-visible spectroscopy was used to monitor the kinetics of nanoparticles formation. UV-visible spectroscopic data and TEM images revealed the formation of bimetallic Au/Ag alloy nanoparticles. Mahogany leaf extract contains various polyhydroxy limonoids which are responsible for the reduction of Au(III) and Ag(I) ions leading to the formation and stabilization of Au and Ag nanopaticles.

Biogenic synthesis of Au and Ag nanoparticles by Indian propolis and its constituents.

In an attempt to find natural, environmentally benign, green-chemical agents for the synthesis of metal nanoparticles, we have demonstrated for the first time the excellent efficiency of ethanol and water extracts of a natural, non-toxic material, Indian propolis and two of its chemical constituents, pinocembrin and galangin in the rapid synthesis of stable Ag and Au nanoparticles having wide spectrum of fascinating morphologies. Both of these two extracts were found to be extremely efficient in the synthesis of Ag and Au nanoparticles under alkaline condition. For a given metal ion precursor, the kinetics of particle synthesis were remarkably similar in all the cases, as it is evident from the absorption spectra monitored over time. Moreover they exhibited similar redox behavior under alkaline condition (pH approximately 10.62). The efficiency of the ethanol and water extracts of Indian propolis towards Ag and Au nanoparticles synthesis was compared with that of naturally occurring hydroxyflavonoids, pinocembrin and galangin isolated from Indian propolis; which are equally efficient in the rapid synthesis of Ag and Au nanoparticles and stabilization of the resultant particles.

Biogenic synthesis of Au and Ag nanoparticles using aqueous solutions of Black Tea leaf extracts.

We explored the application of three different aqueous solutions derived from Black Tea leaf extracts in the synthesis of Au and Ag nanoparticles. The plain tea leaf broth, as well as that containing the ethyl acetate extract of tea leaves, were found to be extremely efficient, leading to rapid formation of stable nanoparticles of various shapes: spheres, trapezoids, prisms and rods. For a given metal ion precursor, the kinetics of particle synthesis were remarkably similar in these two solutions, as evidenced from their absorption spectroscopy monitored over time. Moreover, they exhibited similar redox behavior. In contrast, with the other solution, containing the dichloromethane (CH(2)Cl(2)) extract of tea leaves, we failed to detect any nanoparticle generation under similar reaction conditions. Our results suggest that the reduction of metal ions and stabilization of the resultant particles in the first two solutions involved the same class of biomolecules. We identified these biomolecules as the tea polyphenols, including flavonoids, which were present in comparable amounts in both the tea leaf broth and ethyl acetate extract, but are absent in the CH(2)Cl(2) extract of tea leaves. The efficiency of the tea leaf extracts towards Au and Ag nanoparticle synthesis were compared with that of a naturally occurring hydroxyflavonoid, quercetin.